Interleukin-6 is a multifunctional cytokine produced by a variety of cells. This cytokine controls immune response, the acute phase reaction and hematopiesis, and plays a central role in the host defense mechanisms (Kishimoto et al., Blood, 74, 1-10, 1989). This cytokin acts on various tissues, and exhibits growth induction effects, growth inhibitory effects and differentiation induction effects, depending on the nature of the target cell.
It has been suggested that an abnormal expression of the IL-6 gene is related to the generation of various diseases, particularly autoimmune disease, mesangial proliferative glomerulonephritis and plasmacytoma/myeloma (Hirano et al., Immunol. Today, 11, 443-449, 1990; Clein, B. et al., Eur. Cytokins Net. 1, 193-201, 1990). Accordingly, antibodies which inhibit the function of IL-6 are expected to be useful as therapeutic agents in human patients.
In fact, in clinical research wherein mouse monoclonal antibody to human IL-6 was used to treat terminal patients with plasmacytoma, inhibition of the growth of the plasmacytoma, as well as decreases in the levels of circulating M protein, serum calcium, serum IgG and C-reactive protein were shown (Klein, B. et al., Blood, 78, 1198-1204, 1991; Klein, B. et al., Res. Immunol., 143, 774-776, 1992).
Mouse monoclonal antibodies are highly immunogenic (in other words, "antigenic") in humans, and therefore their therapeutic value in humans is limited. In addition, although mouse monoclonal antibodies may block target activities, they cannot be administered frequently without causing an immune response which results in the danger of an undesirable allergic response.
To solve these problems, processes for the production of humanized antibodies have been developed. Mouse antibodies can be humanized by two processes. The simpler method provides a chimeric antibody comprising variable regions derived from a mouse monoclonal antibody and constant regions derived from a human antibody. The resulting chimeric antibody comprises the entire variable regions of a mouse antibody and would be expected to bind to an antigen with the same specificity as the mouse antibody.
In addition, in a chimeric antibody, the proportion of protein sequence derived from a source other than human is decreased, and therefore its immunogenicity would be expected to be lower than that of a mouse antibody. Although chimeric antibodies bind well to antigens and have a lower antigenicity, there is still a possibility that an immune response to the mouse variable regions will occur (LoBuglio et al., Proc. Natl. Acad. Sci. USA, 84, 4220-4224, 1989).
Although the second process for humanizing a mouse antibody is more complicated, it further lowers the potential immunogenicity of the mouse antibody. In this process, complementarity determining regions (CDRs) from the variable regions of a mouse antibody are transplanted into the variable regions of a human antibody to construct reshaped human antibody variable regions.
Next, these reshaped human variable regions are joined to the constant regions of a human antibody. The only portions derived from a protein sequence other than human protein sequence in the finally reshaped humanized antibody are the CDRs and minor portions of the framework regions (FRs). CDRs are composed of hypervariable protein sequences. They do not represent species-specific sequence. For these reasons, a reshaped human antibody carrying mouse CDRs should not have immunogenicity higher than that of a natural human antibody comprising human CDRs.
For reshaped human antibodies, see further Richmann, L. et al., Nature, 322, 323-327, 1988; Verhoeye, M. et al., Science, 239, 1534-1536, 1988; Kettleborough, C. A. et. al., Protein Engineering. 1, 773-783, 1991; Maeda, H. et al., Human Antibodies and Hybridoma, 2, 124-134, 1991; Gorman, S. G. et al., Proc. Natl. Acad. Sci. USA, SE, 4181-4185, 1991; Tempert, P. R. et al., Bio/Technology, 9, 266-271, 1991; Co, M. S. et al., Proc. Natl. Acad. Sci. USA, 88, 2869-2873, 1991; Carter, P. et al., Proc. Natl. Acad. Sci. USA, 89, 4285-4289, 1992; Co, M. N. et al., J. Immunol. 147, 1149-1154, 1992; and Sato, K. et al., Cancer Res. 53, 1-6, 1993.